Telephone trunk circuits



*Im* .EEZ-1111x155 ETT-.-

A. J. RAY

Filed May 25 i 1. l I l l. Z

TELEPHONE TRUNK CIRCUITS- Tm-Vm-m Y 9 Patented July 15, 1924.

UNITED STATES;

PATENT orties.

ARTHUR J'. RAY,k O F CHICAGO, ILLINOIS, A SSIGNOR TO AUTOMATIC ELECTRIC'CCM- PANY, F CHICAGO, ILLINQIS,

A oonrona'rrou or ILLINOIS.

TELEPHONE 'I'RLTNK CIRCUITS.

Application filed May 25,

To @ZZ 107mm it may con-ccm.' e

Be it known that I, ARTHUR J. RAY, a citizen of the United States of America, and a resident of Chicagm Cook County, and

State of Illinois, have invented certain new and useful Improvements in Telephone Trunk Circuits, of which the following isl a specication.

The present. invention relates in general to telephone trunk circuits and more particularly to suchv trunk. circuits as are adapted to be used in automatic telephone systems. l

In telephone systems where there are a number of small isolated exchanges, coin- -monly known as community automatic exchanges, it is customary toprovide tollv trunk lines going to each of these eXchanges from a toll centre over which toll or long distance connections are established. In small exchanges of the character mentioned aboveone toll trunk extending to each office is usually all that is necessary to handle all toll connections. e l

In such systems it is also customary to have the subscribers in each exchange call the recording operator at the toll cent-re over the toll trunlr line. Under theseconditions it very often happens that the subscribers in the various isolated exchanges have a great deal of diiiculty in calling the recordf ing operator as the toll trunk line extend: ing toeach exchange is usually in use the greater part of the time for toll connections. This diiiiculty could, of course., be obviated by providing an addi-tional toll trunk line going to each of the various isolated exchanges, but it will he appreciated thatl where the exchanges are located at some distance apart this solution would entailk a great deal of expenditure and might not, on account of the small number ot Vtoll connections to the exchange, be an entirely practical one.

The general object of the invention isto do away with :the abovediiiiculty by providing a recording trunk extending to 4the recording toll .operator at the toll centre which is superimposed on the regular .toll trunk, and to so arrange the circuits that even though the toll line ris in use the recording operator may be called kwithout?'interfering with the toll connection.

The above and other ,objects of the .in-g

17921. Serial No.1472f1f284.

vention will be described fully hereinafter with reference to the accompanying' draw# ing.y y 'l Referring now to the drawing, the referencecharacters l2 and a3 indicate the two line conductors of a toll trunk line which terminateat opposite ends in the repeating coils. R1 andR2. The repeating coilIf is located at the toll centre and serves to in'-l ductively connect the toll trunk line to the trunk extending t0. the toll crratr Pcf sition. The toll trunl comprisingconductors @and 43 is connectedinductivelyby means of the repeating coil Rlftothe vconductors 10 and ll which ter'1ninate"in"`the community automatic exchange in an incoming selector switch (not fslown). "This selector has access to connector switches of the usual Strowgsf tyre, which are ,the final switches used for extending connections 'to called lines'inY the isolated exchange; the selector and connector switchesrl in the community automatic Vexchange are of the well known Strowger type, whosei'functio'ns and operations arewelllrnowm and also since they form no' part of thepre'sentinl vention, they have not been 's hownin the drawing.V Y v i The relay group E is arepeater located at the isolated yexchange whose functionit'is to translate the impulses comingin/by way of the toll trunkline 'over a simplex Ycircuit to ordinary two ,wiredmpulses inorderjto control the operation of switches in the exchange. The repeating coils R and. Its form part of the VSimpleXf'circuit of the tollrecording trunk which -is superii'nposed on the toll line. At Athe right, .the repeating coil AR3 "inductively connects ,the superimposed portionof the circuit to the recerding:operatorstrunk circuit which terminates rin the' jack J1, while at the lefttherepeating coilR inductively connects the superimpose'd circuit to the conductors 5 5 and 57." These coinductors terminate lin niu'ltipled bank contacts in' the banks of the cominunityautomatic Yexchange iirst yselectors-"and" are adapted to :be seized' by them underllthecontrol olil callingsub'scribeis who lClQSre yto the recordingioperator.

Ihe relay grouplF isalso a repeater inthe community aumenti@ echansslthe"iCtQatS 0f which haveA been' dss'sd .te sshaltlie les recording operator over the superimposed the toll operator will insert the calling end ot lier cord circuitinto the jack J and operate the calling device key K. By the operation of the key K, the calling device S is renderedl operative to control the switches in the isolated exchange over a circuit extending from battery through the 'impedance coil 45, impulsek springs of the calling device S, springs 51 and 52 of key K, working contact of spring 49 and the said spring, conductor 50, left hand windings of the repeating coil R2, over the trunk conductors 42 and 43 in parallel, right hand windings of'. the repeat-ing coil R1, conductor 20, armature26 and its back contact, and thence through the winding of the line relay 17 to ground. The line relay 17 of the repeater E is energized over this circuit and, upon operating, completes the circuit of the slow acting relay 18 at its armature 33, and at its armature 34 places a bridge across the trunk conductors 10Aand 11 thereby completing a circuit for the line relay o'l the incoming selector switch. This bridge may be traced as follows: Trunk conductor 10, upper leit hand winding of the repeating coil R1, lower winding of the electro polarized relay 19, front contact and armature 34, lower left `hand windingfof the repeating coil R1 to trunk conductor 11. The line relay of the incoming selector switch is energized over this circuit and, upon operating, completes the circuitr of its associated slow acting relay. This slow acting relay operates to prepare the operating circuits of the selector switch in the usual manner. In the repeater E the slow acting relay 13, upon energizing, at its armature 36 completes a circuit for the polarizing winding of the electro polarized relay 19 and at its armatures 37 and 38 prepares certain circuits which will be described later. Tt will be noted that the lower winding of the electro polarized relay 19 was included in the line circuit of the line relay of the incoming selector switch. ,However, the current inthis circuit is not flowing in the proper direction and hence the relay 19 will not be operated.

The toll operator may` now operate her calling device S in accordance with the first digit of the desired subscribers number in the branch exchange. By this operation a series of interruptions is produced in the above traced circuit of the line relay 17 which retracts its armatures a plurality of times in response thereto. At each retraction of its armature 34, the previously traced bridge across the trunk conductors 10 and 11 is opened and the series of interruptions is thus repeated to the line relay of the incoming-selector switch. The line relay ot this switch operates in the usual manner to send a series oit impulses to the vertical magnet` The vertical magnet operates to raise the associated switch wipers to the proper level ot' bank contacts, after which they are ro tated under the control of the rotary magnet and the stepping relay into engagement with the bank contacts associated with the first idle trunk line. Then this occurs, the switching relay of the incoming selector will be energized and will operate to extend the trunk conductors 10 and 11 to the line relay of a local connector switch which has access to the line of the desired substation.

In the repeater E, at each retraction of the armature 33 of the line relay 17, an impulse of current is sent over a circuit extending from ground, by way ot armature 33 and its back contact, front contact and armature 38, armature 29 and its back contact, and thence through the winding oit the slow acting relay 63 in the repeater F to battery. Relay 63 is energized over this circuit and, being slow acting, maintains its armature attracted throughout the series ot impulses and opens at its armatures 7() and 71 the connection of the trunk conductors 55 and 57 with the left hand winding of the repeating coil R. The reason for this latter operation is to prevent any dial impulses being heard by a local subscriber, should one be connected to the trunk conductors 55 and 57 in an attempt to call the recording operator. This will appear fully later.

The toll operator at the toll centre may now operate her calling device S in accordance with the last two digits oit' the desired subscribers number after which she will restore the key K to its normal position. By the operation or' the calling device S two series o'f' interruptions are produced in the circuit of the line relay 17 and the local connector selected by the incoming selector is operated into engagement with the terminals oi' the desired line and the ringing of the called subscriber is automatically initiated. vWhen the key K is restored to normal a circuit may be traced extending from ground through the winding of relay 17 in the repeater E, back con tact and armature 26, conductor 20, right hand windings of the repeating coil R1, trunk conductors 42 and 43 in parallel, left hand windings of the repeating coil R2, conductor 50, spring 49 and its working con tact, springs 52 and 53 of key K, and thence through the winding of the relay 46 to battery. Relay 46, upon energizing, at its armature 44 completes the circuit of the visual 47 which operates and the toll oper- Vator knows that the called subscriber has not answered as yet.

lVhen the desired subscriber answers the ring is cut olf and the battery reversed over the trunk` conductors 10 and 11. This operation reverses the current flowing in the lower winding of the polarized relay 19 and causes the operation of this relay. Relay 19, upon energizing, completes a circuit for the slow acting relay 16 at its armature 39. Relay 16, upon operating, opens the circuit of the line relay7 17 at its armature* 26 and at the front contact of this armature connects the conductor 2O to battery by way of the winding of relay 15. A further result of the energization of relay 16 is that a shunt path is provided around the armature 34 and its front contact to provide against the deenergization of the line relay at armature 28, and also at armature 27 there is a holding circuit completed for the slow acting relay 18, thus the lower winding of the electro polarized relay 19 is still maintained in bridge of the trunk conductors 10 and 11. As the conductor 20 is now connected to battery through the winding of relay 15 the circuit of the relay 46 and the visual 47 at the toll operators position is opened and the visual 47 restores to normal therebyv informing the toll operator of the response of the called subscriber.

The desired toll connection having been established, the operations which take place when a subscriber in the community automatic exchange desires to communicate with the recording` operator at the toll centre will now be described. For this purpose it willbe assumed that this subscriber has removed his receiver and operated his calling device in accordance with the digit of the recording operators number. IVhen the receiver is removed at the calling substation the individual line switch operates to extend the calling subscribers line to an idle first selector switch. In response to the digit of the recording operators number the selector is raised to the proper' level after which it automatically rotates until an idle trunk line is found such as the one shown in the drawing comprising conductors -57, inclusive. In the present case, as there is only one incoming toll trunk, there will be but one recording trunk and all the other bank contacts in the selected level will be busied and if the trunk line comprising conductors 55-57, is idle, it will be the one connected to by the operated selector. If

it is busy, the selector will automatically rotate to give a busy tone to the calling subscriber. It will be assumed that the trunk line comprising conductors 553-57, inclusive, is idle and that the operated selector is rotated into engagement withit. The switching relay of this selector switch will tlienbe energized and will operate to extend the line and release trunk conductors to the trunk line comprising conductors.

55-'57, inclusive. As the conductor 56 is a release trunk conductor there will be a preliminary ground impulse transmitted over it which will extend by way of armature 68 and its back contact, through the winding of the slow acting relay 62 to battery. The kcalling subscribers line will also be extended over trunk conductors 55 and 57 to the upper and lower windings of the line relay 60 of the repeater F. Relay 60, upon energizing, at its armature 67 completes a circuit for the slow acting relay 61. The latter relay, upon energizing, opens the previously traced circuit for the slow acting relay 62 at its armature 68 and at the front contact of this armature operates to establish a holding circuit for the operated selector switch and for the individual line switch of the calling subscriber. Relay 62, upon energizing, at its armature 69 completes the circuit of the slow acting relay 64. The latter relay, upon operating, at armature 76 closes the primary circuit through the induction coil I which extendsfrom the left hand brush of the generator Gen. by way of front contact and armature 76, back contact and armature 78, primary winding of the induction coil to the right hand brush of the generator. The induction coil I interrupts its own primary circuit and induces a very high frequency alternating current in its secondary winding which extends over a circuit from the secondary of the induction coil by way of front contact and armature 75, left hand windings of the repeating coil R, to armature 74 and its front contact. A high frequency current is now induced in the right hand windings of the repeating coil R and flows over a simplex circuit comprising the conductors 42 and 43 of the vtoll trunk in parallel to the left hand windings of the repeating coil R3 to ground. A high frequency current is now induced in the right hand windings of the repeating coil R3 and serves to operate the bridged high frequency alternating current relay 80. Relay 80, upon energizing, opensthe circuit of relay 81 at its armature 84. Relay 81, upon deenergizing connects the generator Gren1 in a circuit to operate the bridged ring down signal 82. The ring down signal 82, upon operating', serves to notify the recording operator that she is being called. It will be seen that there is but a momentary impulse of current sent to the slow acting relay 64 which operates to close the above traced ringing circuit for operating the high frequency alternating current relay 80. The circuitof relay 80 is closed for only a short interval after which the slow acting relay 64 deenergizes and closes a point in the talking circuit. lq

lThe high frequency current sent out by the generator and the induction coil lis sometimes known as a composite ringing current and is of such highfrequeneyythat it has no eiect upon the operation of kthe relays in the repeater E. In response to the operation of the signal 82 the recording operator will answer the call by means of a suitable cord circuit and ascertain what `is desired by the calling subscriber.y The conversation is carried on between the calling subscriber and the recording operator over the superimposed simplex circuit and has no eifect on any connection that may be made on the toll trunk.

It will be noted that should the operator at the toll board be calling over the toll trunk, that is operating her calling device, the instant the trunk line comprising conductors 55-57, inclusive, is seized in the community automatic exchange, that the ring down signal 82 will be operated but the talking circuit between the recording operator and the calling subscriber will be opened at armatures and 71 in the repeater F. This provision is made so that the subscriber calling the recording operator will not hear any of the impulses from ther calling device S and thus be unduly annoyed. f

`When the conversation is terminated between the recording operator and the calling subscriber', the operator will withdraw the answering plug of her cord circuit from the jaclrJ1 and the subscriber will replace his receiver upon the switchhook. Upon the receiver being replaced at the calling substation the relay 60 deenergizes and opens the circuit of the slow acting relay 61. The latter relay deenergizes and removes ground from the release trunk conductor 56 thereby breaking the holding circuitsof the preceding selector and the subscribers line lswitch and allowing these switches to release. All the apparatus in the repeater F is now restored to normal and the recording operator may again be called by any other subscriber in the branch exchange.

Vhen the conversation isinally terminated on the toll line both subscribers will replace their receivers upon their switchhooks. Upon the replacement of the receiver at the called subst-ation the battery flow over the trunk conductors l() and 11 is restored to normal and the electro polarized relay 19 is deenergized. Relay 19, upon retracting its armature 39, opens the circuit of the slow acting relay 16. Relay 16, upon deenergizing, again connects the conductor 20 through the winding of' .the line relay 17 to ground. The line relay 17 is immediately energized in series with the visual 17 associated with the jack J at the toll operators position. Upon operating, relay 17 closesthe circuit of the slow acting relay 18,

which being slow acting has not yet deenergized. The operation of the visual i7 serves to inform the toll operator of the replacement of the receiver at the called substation and she will take down the connection. Then the calling plug is withdrawn from the jack J the circuit of the line relay 17 is opened and this relay deenergizes thereby opening the circuit of the slow acting relay 18, and also removing Y,the lower winding of the electro polarized relay 19 from in bridge of the trunk conductors 10 and 11. By the latter operation the line relay of the local connector switch is deenergized and the connector and selector switches in the branch exchange are thereby released. The relay 18, upon deenergizing, opens the circuit of the polarizing winding oi' the electro polarized relay 19. In the above manner all the apparatus is restored to normal.

It the toll operator should withdraw the plug of her cord circuit from the ack J beiore the called subscriber in the community automatic exchange replaces his receiver upon the switchhook, the relay 15 in the repeater E would be energized. Relay 15, upon operating, opens the holding circuit of the slow acting relay 18. The latter relay, upon deenergizing, removes the lower winding of the polarized relay 19 from in bridge of the trunk conductors 10 and 11 thereby initiating the release of the branch exchange switches in the usual manner and at the same time opens the circuit of the p0- larizing winding of the relay 19. Relay 19, then deenergizes and opens the circuit of the slow acting relay 16, which deenergizes, opening the circuit of the relay 15, which deenergizes also.

Having fully described and ascertained the features of the invention, what is considered to be new and desired to have protected by Letters Patent will be pointed out in the appended claims.

lVhat I claim is:

1. In a telephone system, a toll oh'ice, an automatic exchange, and an interconnecting toll line, automatic switches in the automatic exchange controlled by a toll switching operator in the toll oflice to establish a connection over said toll line, repeating coils, a ground return talking circuit superimposed on said toll line by means of said repeating coils, a recording operators position in the toll o'liice, and other switches in vthe automatic exchange controllable by sublll thereover by an operator at said position for ing operators position, other automatic,

switches in the automatic exchange, said superimposed circuit terminating at the automatic exchange 1n the banks of said other automatic switches, means whereby a subscriber in the automatic exchangecan operate one of said last named switches to connect with the said superimposed circuit, and means for then automatically signalling the recording operator.

3. In a telephone system, a toll lai-ne connecting two exchanges, a superimposed ground return circuit including the two sides of said toll line in parallel, automatic switches in one exchange, a switch control branch and a talking branch of said superimposed circuit at each end thereof, and means for opening one of the talking branches whenever the switch control branches are in use for operating automatic switches.

et. In a telephone system, a toll line connecting two exchanges, a superimposed ground return circuit including the two sides of said toll line in parallel, automatic switches in one exchange, a switch control branch and a talking branch of said superimposed circuit at each end thereof, means for establishing a connection including the said talking branches, means for operating said switches over the said switch control branches to establish a connection including the said toll line, and means for opening the said first connection temporarily while said switches are being operated.

5. In a telephone system, a trunk line extending from a first to a second exchange, means for extending connections over said trunk line, an operators position at said second exchange, a signal at said operators position, a circuit superimposed on said trunk line with which the said signal is associated, an automatic switch operable by a calling subscriber for connecting with said superimposed circuit, means including a slow acting relay for sending a momentary high frequency current over said superimf posed circuit when the connection is established, and means responsive to said high frequency current for operating said signal.

6. In a telephone system, a trunk line connecting two exchanges, a talking circuit between said exchanges including the two conductors of said trunk line in series, a second talking circuit between said exchanges including the two conductors of said trunk line in parallel and ground return, and

means including automatic switches for establishing said talking circuits.

7. In a telephone system, a trunk line connecting two exchanges, a talkingl circuit between said exchanges'including the twoy conductors of said trunk line in series, a second talking circuit between said exchanges in-. cluding the two conductors of said trunk line in parallel and ground return,e1neans including an automatic switch `for establishing the first of said talking circuits, and means including another automatic switch operable whilethe first circuit is in use to establish the second talking circuit. i

8. In a telephone system, a trunk line connecting two exchanges, a talking circuit be tween said exchanges including the two conductors of said trunk line in series, a second talking circuit between said exchanges including the two conductors of saidV trunk line in parallel and ground return, means including an automatic switch controlled over a conductor used in the second talking circuit to establish the first talking circuit, and means including another automatic switch for establishing the second talking circuit while the first is in use.

9. In a telephone system, a trunk line connecting two exchanges, a simplex control circuit superimposed on the two conductors of said trunk line, automatic switches in the first of said exchanges controlled over said simplex circuit from the second exchange to set up an inter-exchange talking circuit over said trunk line, a second trunk line connecting said exchanges utilizing a part of said simplex circuit as one conductor and ground as the other conductor, and another automatic switch in the first exchange locally controlled to set up a talking connection over said second trunk line.

10. In a telephone system, a toll exchange, a toll operators position and a recording operators position in said exchange, an automatic exchange including automatic switches, a trunk line interconnecting said exchanges and terminating in a jack at said toll operators position and in one of said switches at the automatic exchange, a second trunk having one of its conductors superimposed on the conductors of the first trunk in parallel and having for its other conductor ground, said last trunk being accessible to other of said automatic switches in the automatic exchange and terminating in ajack Vat the recording operators position in the toll exchange, means for establishing a talking connection over said first trunk, and means for establishing a talking connection over said second trunk while said first trunk is in use.

11. In a telephone system, a toll exchange, an automatic exchange, a tell line termi-Y nating in a j ack at the toll exchange and in an automatic switch in the automatic ex change, means at the toll exchange for transmitting operating impulses to the automatic exchange over two conductors of said trunk line in parallel to operate said switch to extend talking connections to the automatic exchange, another trunk consisting of a ground return circuit superimposed on said first trunk, automatic switches in the automatic exchange having access to said superimposed trunk, a signal at the toll exchange,

means associated with said superimposed trunk effective fwhen the trunk is seized for operating said signal, and circuit arrangements rfor permitting an operator at the toll exchange to talk to the calling substation in the automatic exchange over saidkk superimposed circuit.

12. In a telephone system, an automatic exchange provided with automatic switches, a toll exchange, a pair of trunks connecting said exchanges, the talking conductors of one of said trunks being divided into three inductively related sections7 the other of said trunks having two sections inductively connected by means of a third section comprising one of the sections ot' said first trunk and ground, means at the toll exchange for transmitting operating impulses over the first trunk for positioning certain of said automatic switches in the automatic exchange to completeV talking connections with subscribers of the toll exchange, subscriber controlled means at the automatic exchange for -causing other of said automatic switches to seize said second trunk, means responsive to such seizure for signalling an operator at the toll exchange, and circuit arrangements for permitting an operatorfat the toll exu change to converse with subscribers in the automatic exchange over said superimposed trunk while the talking circuit is being maintained over the first trunk. Y

In witness whereof, I hereunto subscribe my name this 16th day of May, A. D., 1921.

ARTHUR J. RAY. 

